The immunogenicity of the polyvalent pneumococcal vaccine was studied in renal allograft recipients and dialysis patients. There was no significant overall difference in the antibody response of the allograft recipients compared to control subjects at 1 month following immunization. Chronic hemodialysis patients had significantly lower postvaccination antibody levels for 6 of 12 serotypes. Better graft function in the allograft recipients correlated positively with higher antibody levels. Azathioprine and prednisone in dosages employed had no consistent effect on antibody response. No deterioration of renal function ascribable to the vaccine was observed. Patients were sampled at 1, 2, and 3 1/2 years following immunization. Geometric mean titers (GMT) were calculated for all the serotypes per group for each time of sampling. There was a significant decrease with time in antibody GMTs for all the groups (P less than 0.01). Chronic hemodialysis patients had significantly lower GMTs than control subjects and allograft recipients at 1, 2, and 3 1/2 years postimmunization (P less than 0.05). The 3 1/2 years postimmunization antibody levels were very low in dialysis patients, suggesting that reimmunization of these patients may be required.